This invention relates to incandescent projection lamps and more particularly to such lamps which include a reflector within the lamp's envelope.
It is well known in the projection lamp art to utilize an internal (or proximity) reflector within the lamp's envelope. A hermetically sealed internal reflector is protected against oxidation, dirt, and other adverse conditions typically found in the lamp's environment. Internal reflectors also assure a cooler operating lamp due to the ability of such components to reflect much of the heat from the envelope's rear walls. Perhaps the most significant gain however is in the projection system's screen brightness as a result of the reflector's ability to direct the lamp's output in the substantially singular primary direction.
As will be described, the present invention defines an internal reflector projection lamp which is capable of providing a bidirectional light output. That is, the lamp's output is substantially concentrated in two opposing directions. One particular use for the lamp of the invention is within the projection system described in the aforementioned copending application under Ser. No. 758,988. The overhead projection system in Ser. No. 758,988 utilizes a lens assembly which includes therein a pair of condensing lenses each having a different focal length. It is desired in the system to use a singular light source and to expose the lens assembly to both direct and indirect (reflected) light.